Systems for converting an image or other optically detectable surface condition, such as characters on a document, into electrical signals which can either be stored in memory for later recall or which can be transmitted to a remote location over, for example, telephone communication lines or similar apparatus, are well know in the reproduction art. Systems of this type have generally been referred to as image scanners. In one type of image scanner, the image bearing document is held stationary and a photosensitive element or an array of photosensitive elements, along with a localized source of illumination, is successively scanned across each line of the document. In another type of image scanner, the array of photosensitive elements and the light source are held stationary and the image bearing document is moved therepast. In both types of image scanning systems, as the image-bearing document is scanned, the high optical density or dark portions of the document reflect less light from the light source for reception by the photosensitive elements than the low optical density or light portions. As a result, the high and low optical density portions can be contrasted by the photosensitive elements for photogenerating electrical signals representative of the image on, or other surface characteristic of, the image of the image-bearing document.
While image scanning systems of the type described in the previous paragraph have proven generally successful in fulfilling their intended purposes and have gained commercial acceptability, prior to the invention disclosed in the parent of this application, such optical image scanning systems have exhibited several deficiencies. One major deficiency heretofore encountered in image scanning systems of this type has been the need to employ either an optical array of lenses to focus the light from the image bearing surface onto the array of photosensitive elements, or to locate the image bearing surface in extremely close relationship to the array of photosensitive elements, which elements are then adapted to scan the image on that surface. This close relationship between the image on the image bearing surface and the photosensitive elements was required in order to facilitate the "proximate focusing" of light from a small area portion of the image on the image-bearing surface onto a corresponding small area photosensitive element of the array. This close relationship was necessary because of the fact that light quickly diffuses. Due to that diffusion if the photosensitive elements were not located in close proximity to said small area portions of the image upon the image bearing surface, light emanating from one small area portion thereof would diffuse onto photosensitive elements not corresponding to said small area portion. The result would be the photogeneration of false signals by said small area photosensitive elements, which false signals could result in a replicated image of poor resolution and unacceptable quality.
Heretofore, this necessity for maintaining a close physical relationship between the plane of said array of photosensitive elements and the plane of said image bearing surface could only be satisfied by having said photosensitive elements, and any abrasion resistant, overcoat layer disposed thereupon, actually contact and slide across the image bearing surface. The relative motion between the image bearing surface and the array of photosensitive elements resulted in a second deficiency of prior art image scanning systems; i.e., said deficiency being the build-up of a large static charge on the image bearing surface. Therefore, such prior art systems required that precautions be taken to prevent the static charge built-up on said image bearing surface from inducing an electrical charge in the spacedly positioned array of photosensitive elements, which induced charge (of up to 600 volts) would be capable of deleteriously affecting, and possibly fatally damaging, said photosensitive elements. Previous attempts to solve this problem had focused upon the use of a static shielding operatively layer interposed between the image bearing surface and the array of photosensitive elements. While this approach has proven successful in eliminating the deleterious effects of the build-up of static charge, it has also served to lengthen the distance between the image bearing surface and the array of photosensitive elements, thereby reducing the quality and resolution of the image being photogenerated by the photosensitive elements. The fabrication of the image scanning system with static shielding layer further necessitated additional costs and induced additional fabrication constraints.
In the parent of instant patent application, solutions to the problem of maintaining said photosensitive elements in close proximity to said image bearing surface and solutions to the problem of static build-up were provided. With respect to the question of static build-up, the fiber optic faceplate provided a relatively thick dielectric material between the array of photosensitive elements and the image-bearing surface. Since the faceplate is relatively thick and fabricated of a dielectric material, it provided sufficient electrical isolation between the array and the static electrical charge built up on the image bearing surface being scanned that said static charge was unable to harm the spacedly positioned array of photosensitive elements.
Additionally, the fiber optic faceplate transmits radiation emanating from small area portions of the image on said image bearing document to corresponding small area photosensitive elements with such high resolution and efficiency so as to effectively approximate the presence of a zero thickness window between the image bearing surface and the array of photosensitive elements. Therefore, it was only necessary that the light piping faceplate was placed in sufficient proximity to the image bearing surface to accurately transmit radiation from said small area portions of that surface. Because small area portions of the light piping faceplate receive radiation from only corresponding small area portions of the image on said image-bearing substrate and said faceplate is capable of transmitting radiation incident thereupon virtually without loss to corresponding small area photosensitive elements, it was no longer necessary that said array of photosensitive elements be operatively disposed in such close proximity to said image bearing surface.
While the parent of the instant patent application successfully employed a fiber optic faceplate, in the embodiment disclosed therein, the layers of amorphous silicon alloy material from which the array of photosensitive elements was fabricated, were deposited directly upon the light receiving surface of that faceplate. This was a significant step forward in the art because the loss of light transmitted between the photosensitive elements and the image-bearing surface was thereby minimized. However, a problem arose when the inventors of the parent application sought to employ such an image scanning system to scan image bearing surfaces of large dimensions. The problem arose because the company manufacturing the optical fiber faceplate could only manufacture those faceplates in lengths up to six inches, while normal letterhead and computer paper required at least eight inch acceptability. Therefore, it became necessary to employ an alternate fabrication scheme in order to obtain the advantages enumerated hereinabove with respect to the use of the faceplate. It is to the end of modifying the image scanning scheme disclosed in the parent of the instant application to which this invention is directed.
These and other objects and advantages of the subject invention will become apparent from the perusal of the Detailed Description Of The Invention, the Drawings and the Claims which follow hereinafter.